A Universal Mobile Telecommunication System (UMTS) is a broadband, packet based system for the transmission of text, digitized voice, video and multi-media. It is a highly subscribed to standard for third generation and is generally based on Wideband Coded Division Multiple Access (W-CDMA).
In a UMTS system, the Radio Access Network (UTRAN) is responsible for radio communications with mobile User Equipment (UEs). The UTRAN comprises a plurality of Radio Network Subsystems (RNS), each having a Radio Network Controller (RNC). Each RNC is associated with one or more Node Bs, which operate similarly to a base station transmitter in GSM radio networks. The Node Bs send and receive wireless signals to the plurality of UEs within one or more a cell regions. A number of Node B cells grouped together form a UTRAN Registration Area (URA).
The UTRAN is also responsible for communications with a core network (CN). The core network operates in both the circuit-switched (CS) and the packet-switched (PS) domains. Circuit switched traffic is routed to a Mobile Switching Centre (MSC) in the core network, which is a computer that places the calls, and takes and receives data from the subscriber or from Public Switched Telephone Network (PSTN). Packet data is routed through a Service GPRS Support Node (SGSN) in the core network, which is responsible for the delivery of data packets from and to the UEs within its geographical service area.
For establishing and prioritizing Quality of Service (QoS) for communication between a UE and the CN, radio access bearers (RABs) are set up as specified by the CN. For UMTS, quality classes for RABs come in four types: conversational, streaming, interactive, or background. Each type has a different level of assurance against data loss or corruption.
Despite the QoS of the RABs, in the transfer of data between a RNC and a UE across a radio bearer, errors in the transmission or reception of the data may arise. For example, packet data may be corrupted or delayed due to various disturbances in the switching network or due to system congestion. This loss of data is most readily detected by the UE and UTRAN involving functions of the Radio Link Control (RLC) layer.
The RLC layer is part of Layer 2 in the protocol stack for a UMTS network. The RLC layer provides a number of functions for both user and control data passing between a RNC and a UE, including segmentation and retransmission services. These services can be provided by the RLC layer on variable-length protocol data units (PDUs) received from the Medium Access Protocol (MAC) layer. The service of the RLC layer in the control plane is called a Signaling Radio Bearer (SRB), and the service in the user plane is called a Radio Bearer (RB).
Generally, the term “radio bearer” refers to radio resources assigned between the UE and the UTRAN. And, the term “radio access bearer” generally refers to radio resources assigned between the UE and, e.g., a SGSN (Serving GPRS Service Node). The present disclosure shall, at times, refer to the term radio resource, and such term shall refer, as appropriate, to either or both the radio bearer and/or the radio access bearer.
The RRC configures each instance of the RLC layer to operate in one of three modes: transparent, unacknowledged, or acknowledged mode. In transparent mode, erroneous PDUs can be discarded, and transmission can be streaming without segmentation. In unacknowledged mode, erroneous data that is received is either marked or discarded, but no retransmission performed. In acknowledged mode, the RLC layer provides an assured mode of delivery for PDUs. An automatic repeat request (ARQ) system is followed to check for errors in delivery and to provide retransmissions. Data in the form of PDUs delivered in the acknowledged mode for the RLC are referred to as “RLC AMD PDUs.”
The 3GPP standards currently address the situation of a UE not receiving appropriate acknowledgement from the network after sending RLC AMD PDUs on the uplink. In general, after identifying a problem in not receiving acknowledgement and exhausting its defined attempts at retransmission, the transmitting RLC of the UE sends a RESET command to the receiving RLC. If proper acknowledgement of the RESET does not occur after a certain period of time, the transmitting RLC in the UE identifies a “RLC unrecoverable error.”